Andrey Konovalov [Tue, 19 Dec 2023 22:28:49 +0000 (23:28 +0100)]
kasan: introduce kasan_mempool_unpoison_object
Introduce and document a kasan_mempool_unpoison_object hook.
This hook serves as a replacement for the generic kasan_unpoison_range
that the mempool code relies on right now. mempool will be updated to use
the new hook in one of the following patches.
For now, define the new hook to be identical to kasan_unpoison_range. One
of the following patches will update it to add stack trace collection.
Link: https://lkml.kernel.org/r/dae25f0e18ed8fd50efe509c5b71a0592de5c18d.1703024586.git.andreyknvl@google.com Signed-off-by: Andrey Konovalov <andreyknvl@google.com> Cc: Alexander Lobakin <alobakin@pm.me> Cc: Alexander Potapenko <glider@google.com> Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com> Cc: Breno Leitao <leitao@debian.org> Cc: Dmitry Vyukov <dvyukov@google.com> Cc: Evgenii Stepanov <eugenis@google.com> Cc: Marco Elver <elver@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Andrey Konovalov [Tue, 19 Dec 2023 22:28:48 +0000 (23:28 +0100)]
kasan: add return value for kasan_mempool_poison_object
Add a return value for kasan_mempool_poison_object that lets the caller
know whether the allocation is affected by a double-free or an
invalid-free bug. The caller can use this return value to stop operating
on the object.
Also introduce a check_page_allocation helper function to improve the code
readability.
Link: https://lkml.kernel.org/r/618af65273875fb9f56954285443279b15f1fcd9.1703024586.git.andreyknvl@google.com Signed-off-by: Andrey Konovalov <andreyknvl@google.com> Cc: Alexander Lobakin <alobakin@pm.me> Cc: Alexander Potapenko <glider@google.com> Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com> Cc: Breno Leitao <leitao@debian.org> Cc: Dmitry Vyukov <dvyukov@google.com> Cc: Evgenii Stepanov <eugenis@google.com> Cc: Marco Elver <elver@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Andrey Konovalov [Tue, 19 Dec 2023 22:28:45 +0000 (23:28 +0100)]
kasan: rename kasan_slab_free_mempool to kasan_mempool_poison_object
Patch series "kasan: save mempool stack traces".
This series updates KASAN to save alloc and free stack traces for
secondary-level allocators that cache and reuse allocations internally
instead of giving them back to the underlying allocator (e.g. mempool).
As a part of this change, introduce and document a set of KASAN hooks:
Besides mempool, skbuff and io_uring also cache allocations and already
use KASAN hooks to poison those. Their code is updated to use the new
mempool hooks.
The new hooks save alloc and free stack traces (for normal kmalloc and
slab objects; stack traces for large kmalloc objects and page_alloc are
not supported by KASAN yet), improve the readability of the users' code,
and also allow the users to prevent double-free and invalid-free bugs; see
the patches for the details.
This patch (of 21):
Rename kasan_slab_free_mempool to kasan_mempool_poison_object.
kasan_slab_free_mempool is a slightly confusing name: it is unclear
whether this function poisons the object when it is freed into mempool or
does something when the object is freed from mempool to the underlying
allocator.
The new name also aligns with other mempool-related KASAN hooks added in
the following patches in this series.
Matthew Wilcox (Oracle) [Fri, 15 Dec 2023 20:02:45 +0000 (20:02 +0000)]
fs: remove the bh_end_io argument from __block_write_full_folio
All callers are passing end_buffer_async_write as this argument, so we can
hardcode references to it within __block_write_full_folio(). That lets us
make end_buffer_async_write() static.
Link: https://lkml.kernel.org/r/20231215200245.748418-15-willy@infradead.org Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org> Reviewed-by: Jens Axboe <axboe@kernel.dk> Reviewed-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Matthew Wilcox (Oracle) [Fri, 15 Dec 2023 20:02:44 +0000 (20:02 +0000)]
fs: convert block_write_full_page to block_write_full_folio
Convert the function to be compatible with writepage_t so that it can be
passed to write_cache_pages() by blkdev. This removes a call to
compound_head(). We can also remove the function export as both callers
are built-in.
Link: https://lkml.kernel.org/r/20231215200245.748418-14-willy@infradead.org Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org> Reviewed-by: Christoph Hellwig <hch@lst.de> Reviewed-by: Jens Axboe <axboe@kernel.dk> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Matthew Wilcox (Oracle) [Fri, 15 Dec 2023 20:02:35 +0000 (20:02 +0000)]
fs: reduce stack usage in do_mpage_readpage
Some architectures support a very large PAGE_SIZE, so instead of the 8
pointers we see with a 4kB PAGE_SIZE, we can see 128 pointers with 64kB or
so many on Hexagon that it trips compiler warnings about exceeding stack
frame size.
All we're doing with this array is checking for block contiguity, which we
can as well do by remembering the address of the first block in the page
and checking this block is at the appropriate offset from that address.
Link: https://lkml.kernel.org/r/20231215200245.748418-5-willy@infradead.org Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org> Reviewed-by: Christoph Hellwig <hch@lst.de> Reviewed-by: Jens Axboe <axboe@kernel.dk> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Matthew Wilcox (Oracle) [Fri, 15 Dec 2023 20:02:34 +0000 (20:02 +0000)]
fs: reduce stack usage in __mpage_writepage
Some architectures support a very large PAGE_SIZE, so instead of the 8
pointers we see with a 4kB PAGE_SIZE, we can see 128 pointers with 64kB or
so many on Hexagon that it trips compiler warnings about exceeding stack
frame size.
All we're doing with this array is checking for block contiguity, which we
can as well do by remembering the address of the first block in the page
and checking this block is at the appropriate offset from that address.
Link: https://lkml.kernel.org/r/20231215200245.748418-4-willy@infradead.org Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org> Reviewed-by: Christoph Hellwig <hch@lst.de> Reviewed-by: Jens Axboe <axboe@kernel.dk> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Matthew Wilcox (Oracle) [Fri, 15 Dec 2023 20:02:32 +0000 (20:02 +0000)]
fs: remove clean_page_buffers()
Patch series "Clean up the writeback paths".
Most of these patches verge on the trivial, converting filesystems that
just use block_write_full_page() to use mpage_writepages(). But as we saw
with Christoph's earlier patchset, there can be some "interesting"
gotchas, and I clearly haven't tested the majority of filesystems I've
touched here.
Patches 3 & 4 get rid of a lot of stack usage on architectures with larger
page sizes; 1024 bytes on 64-bit systems with 64KiB pages. It starts to
open the door to larger folio sizes on all architectures, but it's
certainly not enough yet.
Patch 14 is kind of trivial, but it's nice to get that simplification in.
This patch (of 14):
This function has been unused since the removal of bdev_write_page().
After analyzing the vmcore, I found this issue is caused by page migration.
The scenario is that, one thread is doing page migration, and we will use the
target page's ->mapping field to save 'anon_vma' pointer between page unmap and
page move, and now the target page is locked and refcount is 1.
Currently, there is another stress-ng thread performing memory hotplug,
attempting to offline the target page that is being migrated. It discovers that
the refcount of this target page is 1, preventing the offline operation, thus
proceeding to dump the page. However, page_mapping() of the target page may
return an incorrect file mapping to crash the system in dump_mapping(), since
the target page->mapping only saves 'anon_vma' pointer without setting
PAGE_MAPPING_ANON flag.
There are seveval ways to fix this issue:
(1) Setting the PAGE_MAPPING_ANON flag for target page's ->mapping when saving
'anon_vma', but this can confuse PageAnon() for PFN walkers, since the target
page has not built mappings yet.
(2) Getting the page lock to call page_mapping() in __dump_page() to avoid crashing
the system, however, there are still some PFN walkers that call page_mapping()
without holding the page lock, such as compaction.
(3) Using target page->private field to save the 'anon_vma' pointer and 2 bits
page state, just as page->mapping records an anonymous page, which can remove
the page_mapping() impact for PFN walkers and also seems a simple way.
So I choose option 3 to fix this issue, and this can also fix other potential
issues for PFN walkers, such as compaction.
Link: https://lkml.kernel.org/r/e60b17a88afc38cb32f84c3e30837ec70b343d2b.1702641709.git.baolin.wang@linux.alibaba.com Fixes: 64c8902ed441 ("migrate_pages: split unmap_and_move() to _unmap() and _move()") Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com> Reviewed-by: "Huang, Ying" <ying.huang@intel.com> Cc: Matthew Wilcox <willy@infradead.org> Cc: David Hildenbrand <david@redhat.com> Cc: Xu Yu <xuyu@linux.alibaba.com> Cc: Zi Yan <ziy@nvidia.com> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Matthew Wilcox (Oracle) [Wed, 13 Dec 2023 21:58:42 +0000 (21:58 +0000)]
mm: convert swap_cluster_readahead and swap_vma_readahead to return a folio
shmem_swapin_cluster() immediately converts the page back to a folio, and
swapin_readahead() may as well call folio_file_page() once instead of
having each function call it.
Matthew Wilcox (Oracle) [Wed, 13 Dec 2023 21:58:30 +0000 (21:58 +0000)]
mm: return the folio from __read_swap_cache_async()
Patch series "More swap folio conversions".
These all seem like fairly straightforward conversions to me. A lot of
compound_head() calls get removed. And page_swap_info(), which is nice.
This patch (of 13):
Move the folio->page conversion into the callers that actually want that.
Most of the callers are happier with the folio anyway. If the
page_allocated boolean is set, the folio allocated is of order-0, so it is
safe to pass the page directly to swap_readpage().
Chengming Zhou [Thu, 28 Dec 2023 09:45:46 +0000 (09:45 +0000)]
mm/zswap: change per-cpu mutex and buffer to per-acomp_ctx
First of all, we need to rename acomp_ctx->dstmem field to buffer, since
we are now using for purposes other than compression.
Then we change per-cpu mutex and buffer to per-acomp_ctx, since them
belong to the acomp_ctx and are necessary parts when used in the
compress/decompress contexts.
So we can remove the old per-cpu mutex and dstmem.
Link: https://lkml.kernel.org/r/20231213-zswap-dstmem-v5-5-9382162bbf05@bytedance.com Signed-off-by: Chengming Zhou <zhouchengming@bytedance.com> Acked-by: Chris Li <chrisl@kernel.org> (Google) Reviewed-by: Nhat Pham <nphamcs@gmail.com> Cc: Barry Song <21cnbao@gmail.com> Cc: Dan Streetman <ddstreet@ieee.org> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Seth Jennings <sjenning@redhat.com> Cc: Vitaly Wool <vitaly.wool@konsulko.com> Cc: Yosry Ahmed <yosryahmed@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Chengming Zhou [Thu, 28 Dec 2023 09:45:43 +0000 (09:45 +0000)]
mm/zswap: refactor out __zswap_load()
zswap_load() and zswap_writeback_entry() have the same part that
decompress the data from zswap_entry to page, so refactor out the common
part as __zswap_load(entry, page).
Link: https://lkml.kernel.org/r/20231213-zswap-dstmem-v5-2-9382162bbf05@bytedance.com Signed-off-by: Chengming Zhou <zhouchengming@bytedance.com> Reviewed-by: Nhat Pham <nphamcs@gmail.com> Reviewed-by: Yosry Ahmed <yosryahmed@google.com> Acked-by: Chris Li <chrisl@kernel.org> (Google) Cc: Barry Song <21cnbao@gmail.com> Cc: Dan Streetman <ddstreet@ieee.org> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Seth Jennings <sjenning@redhat.com> Cc: Vitaly Wool <vitaly.wool@konsulko.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Chengming Zhou [Thu, 28 Dec 2023 09:45:42 +0000 (09:45 +0000)]
mm/zswap: reuse dstmem when decompress
Patch series "mm/zswap: dstmem reuse optimizations and cleanups", v5.
The problem this series tries to optimize is that zswap_load() and
zswap_writeback_entry() have to malloc a temporary memory to support
!zpool_can_sleep_mapped(). We can avoid it by reusing the percpu
crypto_acomp_ctx->dstmem, which is also used by zswap_store() and
protected by the same percpu crypto_acomp_ctx->mutex.
This patch (of 5):
In the !zpool_can_sleep_mapped() case such as zsmalloc, we need to first
copy the entry->handle memory to a temporary memory, which is allocated
using kmalloc.
Obviously we can reuse the per-compressor dstmem to avoid allocating every
time, since it's percpu-compressor and protected in percpu mutex.
Stefan Roesch [Mon, 18 Dec 2023 23:10:54 +0000 (15:10 -0800)]
mm/ksm: document ksm advisor and its sysfs knobs
This documents the KSM advisor and its new knobs in /sys/fs/kernel/mm.
Link: https://lkml.kernel.org/r/20231218231054.1625219-5-shr@devkernel.io Signed-off-by: Stefan Roesch <shr@devkernel.io> Acked-by: David Hildenbrand <david@redhat.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Rik van Riel <riel@surriel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Stefan Roesch [Mon, 18 Dec 2023 23:10:53 +0000 (15:10 -0800)]
mm/ksm: add tracepoint for ksm advisor
This adds a new tracepoint for the ksm advisor. It reports the last scan
time, the new setting of the pages_to_scan parameter and the average cpu
percent usage of the ksmd background thread for the last scan.
Link: https://lkml.kernel.org/r/20231218231054.1625219-4-shr@devkernel.io Signed-off-by: Stefan Roesch <shr@devkernel.io> Acked-by: David Hildenbrand <david@redhat.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Rik van Riel <riel@surriel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Stefan Roesch [Mon, 18 Dec 2023 23:10:52 +0000 (15:10 -0800)]
mm/ksm: add sysfs knobs for advisor
This adds four new knobs for the KSM advisor to influence its behaviour.
The knobs are:
- advisor_mode:
none: no advisor (default)
scan-time: scan time advisor
- advisor_max_cpu: 70 (default, cpu usage percent)
- advisor_min_pages_to_scan: 500 (default)
- advisor_max_pages_to_scan: 30000 (default)
- advisor_target_scan_time: 200 (default in seconds)
The new values will take effect on the next scan round.
Link: https://lkml.kernel.org/r/20231218231054.1625219-3-shr@devkernel.io Signed-off-by: Stefan Roesch <shr@devkernel.io> Acked-by: David Hildenbrand <david@redhat.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Rik van Riel <riel@surriel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Stefan Roesch [Mon, 18 Dec 2023 23:10:51 +0000 (15:10 -0800)]
mm/ksm: add ksm advisor
Patch series "mm/ksm: Add ksm advisor", v5.
What is the KSM advisor?
=========================
The ksm advisor automatically manages the pages_to_scan setting to achieve
a target scan time. The target scan time defines how many seconds it
should take to scan all the candidate KSM pages. In other words the
pages_to_scan rate is changed by the advisor to achieve the target scan
time.
Why do we need a KSM advisor?
==============================
The number of candidate pages for KSM is dynamic. It can often be
observed that during the startup of an application more candidate pages
need to be processed. Without an advisor the pages_to_scan parameter
needs to be sized for the maximum number of candidate pages. With the
scan time advisor the pages_to_scan parameter based can be changed based
on demand.
Algorithm
==========
The algorithm calculates the change value based on the target scan time
and the previous scan time. To avoid pertubations an exponentially
weighted moving average is applied.
The algorithm has a max and min
value to:
- guarantee responsiveness to changes
- to limit CPU resource consumption
Parameters to influence the KSM scan advisor
=============================================
The respective parameters are:
- ksm_advisor_mode
0: None (default), 1: scan time advisor
- ksm_advisor_target_scan_time
how many seconds a scan should of all candidate pages take
- ksm_advisor_max_cpu
upper limit for the cpu usage in percent of the ksmd background thread
The initial value and the max value for the pages_to_scan parameter can
be limited with:
- ksm_advisor_min_pages_to_scan
minimum value for pages_to_scan per batch
- ksm_advisor_max_pages_to_scan
maximum value for pages_to_scan per batch
The default settings for the above two parameters should be suitable for
most workloads.
The parameters are exposed as knobs in /sys/kernel/mm/ksm. By default the
scan time advisor is disabled.
Currently there are two advisors:
- none and
- scan-time.
Resource savings
=================
Tests with various workloads have shown considerable CPU savings. Most
of the workloads I have investigated have more candidate pages during
startup. Once the workload is stable in terms of memory, the number of
candidate pages is reduced. Without the advisor, the pages_to_scan needs
to be sized for the maximum number of candidate pages. So having this
advisor definitely helps in reducing CPU consumption.
For the instagram workload, the advisor achieves a 25% CPU reduction.
Once the memory is stable, the pages_to_scan parameter gets reduced to
about 40% of its max value.
The new advisor works especially well if the smart scan feature is also
enabled.
How is defining a target scan time better?
===========================================
For an administrator it is more logical to set a target scan time.. The
administrator can determine how many pages are scanned on each scan.
Therefore setting a target scan time makes more sense.
In addition the administrator might have a good idea about the memory
sizing of its respective workloads.
Setting cpu limits is easier than setting The pages_to_scan parameter. The
pages_to_scan parameter is per batch. For the administrator it is difficult
to set the pages_to_scan parameter.
Tracing
=======
A new tracing event has been added for the scan time advisor. The new
trace event is called ksm_advisor. It reports the scan time, the new
pages_to_scan setting and the cpu usage of the ksmd background thread.
Other approaches
=================
Approach 1: Adapt pages_to_scan after processing each batch. If KSM
merges pages, increase the scan rate, if less KSM pages, reduce the
the pages_to_scan rate. This doesn't work too well. While it increases
the pages_to_scan for a short period, but generally it ends up with a
too low pages_to_scan rate.
Approach 2: Adapt pages_to_scan after each scan. The problem with that
approach is that the calculated scan rate tends to be high. The more
aggressive KSM scans, the more pages it can de-duplicate.
There have been earlier attempts at an advisor:
propose auto-run mode of ksm and its tests
(https://marc.info/?l=linux-mm&m=166029880214485&w=2)
This patch (of 5):
This adds the ksm advisor. The ksm advisor automatically manages the
pages_to_scan setting to achieve a target scan time. The target scan time
defines how many seconds it should take to scan all the candidate KSM
pages. In other words the pages_to_scan rate is changed by the advisor to
achieve the target scan time. The algorithm has a max and min value to:
- guarantee responsiveness to changes
- limit CPU resource consumption
The respective parameters are:
- ksm_advisor_target_scan_time (how many seconds a scan should take)
- ksm_advisor_max_cpu (maximum value for cpu percent usage)
- ksm_advisor_min_pages (minimum value for pages_to_scan per batch)
- ksm_advisor_max_pages (maximum value for pages_to_scan per batch)
The algorithm calculates the change value based on the target scan time
and the previous scan time. To avoid pertubations an exponentially
weighted moving average is applied.
The advisor is managed by two main parameters: target scan time,
cpu max time for the ksmd background thread. These parameters determine
how aggresive ksmd scans.
In addition there are min and max values for the pages_to_scan parameter
to make sure that its initial and max values are not set too low or too
high. This ensures that it is able to react to changes quickly enough.
The default values are:
- target scan time: 200 secs
- max cpu: 70%
- min pages: 500
- max pages: 30000
By default the advisor is disabled. Currently there are two advisors:
none and scan-time.
Tests with various workloads have shown considerable CPU savings. Most of
the workloads I have investigated have more candidate pages during
startup, once the workload is stable in terms of memory, the number of
candidate pages is reduced. Without the advisor, the pages_to_scan needs
to be sized for the maximum number of candidate pages. So having this
advisor definitely helps in reducing CPU consumption.
For the instagram workload, the advisor achieves a 25% CPU reduction.
Once the memory is stable, the pages_to_scan parameter gets reduced to
about 40% of its max value.
Matthew Wilcox (Oracle) [Mon, 11 Dec 2023 16:22:10 +0000 (16:22 +0000)]
mm: remove stale example from comment
folio_add_new_anon_rmap() no longer works this way, so just remove the
entire example.
Link: https://lkml.kernel.org/r/20231211162214.2146080-6-willy@infradead.org Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org> Reviewed-by: David Hildenbrand <david@redhat.com> Cc: Ralph Campbell <rcampbell@nvidia.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Matthew Wilcox (Oracle) [Mon, 11 Dec 2023 16:22:09 +0000 (16:22 +0000)]
mm: remove some calls to page_add_new_anon_rmap()
We already have the folio in these functions, we just need to use it.
folio_add_new_anon_rmap() didn't exist at the time they were converted to
folios.
Matthew Wilcox (Oracle) [Mon, 11 Dec 2023 16:22:06 +0000 (16:22 +0000)]
mm: convert ksm_might_need_to_copy() to work on folios
Patch series "Finish two folio conversions".
Most callers of page_add_new_anon_rmap() and
lru_cache_add_inactive_or_unevictable() have been converted to their folio
equivalents, but there are still a few stragglers. There's a bit of
preparatory work in ksm and unuse_pte(), but after that it's pretty
mechanical.
This patch (of 9):
Accept a folio as an argument and return a folio result. Removes a call
to compound_head() in do_swap_page(), and prevents folio & page from
getting out of sync in unuse_pte().
Suren Baghdasaryan [Wed, 6 Dec 2023 10:36:59 +0000 (02:36 -0800)]
selftests/mm: add UFFDIO_MOVE ioctl test
Add tests for new UFFDIO_MOVE ioctl which uses uffd to move source into
destination buffer while checking the contents of both after the move.
After the operation the content of the destination buffer should match the
original source buffer's content while the source buffer should be zeroed.
Separate tests are designed for PMD aligned and unaligned cases because
they utilize different code paths in the kernel.
Link: https://lkml.kernel.org/r/20231206103702.3873743-6-surenb@google.com Signed-off-by: Suren Baghdasaryan <surenb@google.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Axel Rasmussen <axelrasmussen@google.com> Cc: Brian Geffon <bgeffon@google.com> Cc: Christian Brauner <brauner@kernel.org> Cc: David Hildenbrand <david@redhat.com> Cc: Hugh Dickins <hughd@google.com> Cc: Jann Horn <jannh@google.com> Cc: Kalesh Singh <kaleshsingh@google.com> Cc: Liam R. Howlett <Liam.Howlett@oracle.com> Cc: Lokesh Gidra <lokeshgidra@google.com> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Michal Hocko <mhocko@suse.com> Cc: Mike Rapoport (IBM) <rppt@kernel.org> Cc: Nicolas Geoffray <ngeoffray@google.com> Cc: Peter Xu <peterx@redhat.com> Cc: Ryan Roberts <ryan.roberts@arm.com> Cc: Shuah Khan <shuah@kernel.org> Cc: ZhangPeng <zhangpeng362@huawei.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Suren Baghdasaryan [Wed, 6 Dec 2023 10:36:58 +0000 (02:36 -0800)]
selftests/mm: add uffd_test_case_ops to allow test case-specific operations
Currently each test can specify unique operations using uffd_test_ops,
however these operations are per-memory type and not per-test. Add
uffd_test_case_ops which each test case can customize for its own needs
regardless of the memory type being used. Pre- and post-allocation
operations are added, some of which will be used in the next patch to
implement test-specific operations like madvise after memory is allocated
but before it is accessed.
Link: https://lkml.kernel.org/r/20231206103702.3873743-5-surenb@google.com Signed-off-by: Suren Baghdasaryan <surenb@google.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Axel Rasmussen <axelrasmussen@google.com> Cc: Brian Geffon <bgeffon@google.com> Cc: Christian Brauner <brauner@kernel.org> Cc: David Hildenbrand <david@redhat.com> Cc: Hugh Dickins <hughd@google.com> Cc: Jann Horn <jannh@google.com> Cc: Kalesh Singh <kaleshsingh@google.com> Cc: Liam R. Howlett <Liam.Howlett@oracle.com> Cc: Lokesh Gidra <lokeshgidra@google.com> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Michal Hocko <mhocko@suse.com> Cc: Mike Rapoport (IBM) <rppt@kernel.org> Cc: Nicolas Geoffray <ngeoffray@google.com> Cc: Peter Xu <peterx@redhat.com> Cc: Ryan Roberts <ryan.roberts@arm.com> Cc: Shuah Khan <shuah@kernel.org> Cc: ZhangPeng <zhangpeng362@huawei.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Suren Baghdasaryan [Wed, 6 Dec 2023 10:36:57 +0000 (02:36 -0800)]
selftests/mm: call uffd_test_ctx_clear at the end of the test
uffd_test_ctx_clear() is being called from uffd_test_ctx_init() to unmap
areas used in the previous test run. This approach is problematic because
while unmapping areas uffd_test_ctx_clear() uses page_size and nr_pages
which might differ from one test run to another. Fix this by calling
uffd_test_ctx_clear() after each test is done.
Link: https://lkml.kernel.org/r/20231206103702.3873743-4-surenb@google.com Signed-off-by: Suren Baghdasaryan <surenb@google.com> Reviewed-by: Peter Xu <peterx@redhat.com> Reviewed-by: Axel Rasmussen <axelrasmussen@google.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Brian Geffon <bgeffon@google.com> Cc: Christian Brauner <brauner@kernel.org> Cc: David Hildenbrand <david@redhat.com> Cc: Hugh Dickins <hughd@google.com> Cc: Jann Horn <jannh@google.com> Cc: Kalesh Singh <kaleshsingh@google.com> Cc: Liam R. Howlett <Liam.Howlett@oracle.com> Cc: Lokesh Gidra <lokeshgidra@google.com> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Michal Hocko <mhocko@suse.com> Cc: Mike Rapoport (IBM) <rppt@kernel.org> Cc: Nicolas Geoffray <ngeoffray@google.com> Cc: Ryan Roberts <ryan.roberts@arm.com> Cc: Shuah Khan <shuah@kernel.org> Cc: ZhangPeng <zhangpeng362@huawei.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Andrea Arcangeli [Wed, 6 Dec 2023 10:36:56 +0000 (02:36 -0800)]
userfaultfd: UFFDIO_MOVE uABI
Implement the uABI of UFFDIO_MOVE ioctl.
UFFDIO_COPY performs ~20% better than UFFDIO_MOVE when the application
needs pages to be allocated [1]. However, with UFFDIO_MOVE, if pages are
available (in userspace) for recycling, as is usually the case in heap
compaction algorithms, then we can avoid the page allocation and memcpy
(done by UFFDIO_COPY). Also, since the pages are recycled in the
userspace, we avoid the need to release (via madvise) the pages back to
the kernel [2].
We see over 40% reduction (on a Google pixel 6 device) in the compacting
thread's completion time by using UFFDIO_MOVE vs. UFFDIO_COPY. This was
measured using a benchmark that emulates a heap compaction implementation
using userfaultfd (to allow concurrent accesses by application threads).
More details of the usecase are explained in [2]. Furthermore,
UFFDIO_MOVE enables moving swapped-out pages without touching them within
the same vma. Today, it can only be done by mremap, however it forces
splitting the vma.
UFFDIO_MOVE
(Since Linux xxx) Move a continuous memory chunk into the
userfault registered range and optionally wake up the blocked
thread. The source and destination addresses and the number of
bytes to move are specified by the src, dst, and len fields of
the uffdio_move structure pointed to by argp:
struct uffdio_move {
__u64 dst; /* Destination of move */
__u64 src; /* Source of move */
__u64 len; /* Number of bytes to move */
__u64 mode; /* Flags controlling behavior of move */
__s64 move; /* Number of bytes moved, or negated error */
};
The following value may be bitwise ORed in mode to change the
behavior of the UFFDIO_MOVE operation:
UFFDIO_MOVE_MODE_DONTWAKE
Do not wake up the thread that waits for page-fault
resolution
UFFDIO_MOVE_MODE_ALLOW_SRC_HOLES
Allow holes in the source virtual range that is being moved.
When not specified, the holes will result in ENOENT error.
When specified, the holes will be accounted as successfully
moved memory. This is mostly useful to move hugepage aligned
virtual regions without knowing if there are transparent
hugepages in the regions or not, but preventing the risk of
having to split the hugepage during the operation.
The move field is used by the kernel to return the number of
bytes that was actually moved, or an error (a negated errno-
style value). If the value returned in move doesn't match the
value that was specified in len, the operation fails with the
error EAGAIN. The move field is output-only; it is not read by
the UFFDIO_MOVE operation.
The operation may fail for various reasons. Usually, remapping of
pages that are not exclusive to the given process fail; once KSM
might deduplicate pages or fork() COW-shares pages during fork()
with child processes, they are no longer exclusive. Further, the
kernel might only perform lightweight checks for detecting whether
the pages are exclusive, and return -EBUSY in case that check fails.
To make the operation more likely to succeed, KSM should be
disabled, fork() should be avoided or MADV_DONTFORK should be
configured for the source VMA before fork().
This ioctl(2) operation returns 0 on success. In this case, the
entire area was moved. On error, -1 is returned and errno is
set to indicate the error. Possible errors include:
EAGAIN The number of bytes moved (i.e., the value returned in
the move field) does not equal the value that was
specified in the len field.
EINVAL Either dst or len was not a multiple of the system page
size, or the range specified by src and len or dst and len
was invalid.
EINVAL An invalid bit was specified in the mode field.
ENOENT
The source virtual memory range has unmapped holes and
UFFDIO_MOVE_MODE_ALLOW_SRC_HOLES is not set.
EEXIST
The destination virtual memory range is fully or partially
mapped.
EBUSY
The pages in the source virtual memory range are either
pinned or not exclusive to the process. The kernel might
only perform lightweight checks for detecting whether the
pages are exclusive. To make the operation more likely to
succeed, KSM should be disabled, fork() should be avoided
or MADV_DONTFORK should be configured for the source virtual
memory area before fork().
ENOMEM Allocating memory needed for the operation failed.
ESRCH
The target process has exited at the time of a UFFDIO_MOVE
operation.
Link: https://lkml.kernel.org/r/20231206103702.3873743-3-surenb@google.com Signed-off-by: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: Suren Baghdasaryan <surenb@google.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Axel Rasmussen <axelrasmussen@google.com> Cc: Brian Geffon <bgeffon@google.com> Cc: Christian Brauner <brauner@kernel.org> Cc: David Hildenbrand <david@redhat.com> Cc: Hugh Dickins <hughd@google.com> Cc: Jann Horn <jannh@google.com> Cc: Kalesh Singh <kaleshsingh@google.com> Cc: Liam R. Howlett <Liam.Howlett@oracle.com> Cc: Lokesh Gidra <lokeshgidra@google.com> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Michal Hocko <mhocko@suse.com> Cc: Mike Rapoport (IBM) <rppt@kernel.org> Cc: Nicolas Geoffray <ngeoffray@google.com> Cc: Peter Xu <peterx@redhat.com> Cc: Ryan Roberts <ryan.roberts@arm.com> Cc: Shuah Khan <shuah@kernel.org> Cc: ZhangPeng <zhangpeng362@huawei.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Andrea Arcangeli [Wed, 6 Dec 2023 10:36:55 +0000 (02:36 -0800)]
mm/rmap: support move to different root anon_vma in folio_move_anon_rmap()
Patch series "userfaultfd move option", v6.
This patch series introduces UFFDIO_MOVE feature to userfaultfd, which has
long been implemented and maintained by Andrea in his local tree [1], but
was not upstreamed due to lack of use cases where this approach would be
better than allocating a new page and copying the contents. Previous
upstraming attempts could be found at [6] and [7].
UFFDIO_COPY performs ~20% better than UFFDIO_MOVE when the application
needs pages to be allocated [2]. However, with UFFDIO_MOVE, if pages are
available (in userspace) for recycling, as is usually the case in heap
compaction algorithms, then we can avoid the page allocation and memcpy
(done by UFFDIO_COPY). Also, since the pages are recycled in the
userspace, we avoid the need to release (via madvise) the pages back to
the kernel [3]. We see over 40% reduction (on a Google pixel 6 device) in
the compacting thread's completion time by using UFFDIO_MOVE vs.
UFFDIO_COPY. This was measured using a benchmark that emulates a heap
compaction implementation using userfaultfd (to allow concurrent accesses
by application threads). More details of the usecase are explained in
[3].
Furthermore, UFFDIO_MOVE enables moving swapped-out pages without
touching them within the same vma. Today, it can only be done by mremap,
however it forces splitting the vma.
TODOs for follow-up improvements:
- cross-mm support. Known differences from single-mm and missing pieces:
- memcg recharging (might need to isolate pages in the process)
- mm counters
- cross-mm deposit table moves
- cross-mm test
- document the address space where src and dest reside in struct
uffdio_move
- TLB flush batching. Will require extensive changes to PTL locking in
move_pages_pte(). OTOH that might let us reuse parts of mremap code.
This patch (of 5):
For now, folio_move_anon_rmap() was only used to move a folio to a
different anon_vma after fork(), whereby the root anon_vma stayed
unchanged. For that, it was sufficient to hold the folio lock when
calling folio_move_anon_rmap().
However, we want to make use of folio_move_anon_rmap() to move folios
between VMAs that have a different root anon_vma. As folio_referenced()
performs an RMAP walk without holding the folio lock but only holding the
anon_vma in read mode, holding the folio lock is insufficient.
When moving to an anon_vma with a different root anon_vma, we'll have to
hold both, the folio lock and the anon_vma lock in write mode.
Consequently, whenever we succeeded in folio_lock_anon_vma_read() to
read-lock the anon_vma, we have to re-check if the mapping was changed in
the meantime. If that was the case, we have to retry.
Note that folio_move_anon_rmap() must only be called if the anon page is
exclusive to a process, and must not be called on KSM folios.
This is a preparation for UFFDIO_MOVE, which will hold the folio lock, the
anon_vma lock in write mode, and the mmap_lock in read mode.
Link: https://lkml.kernel.org/r/20231206103702.3873743-1-surenb@google.com Link: https://lkml.kernel.org/r/20231206103702.3873743-2-surenb@google.com Signed-off-by: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: Suren Baghdasaryan <surenb@google.com> Acked-by: Peter Xu <peterx@redhat.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Axel Rasmussen <axelrasmussen@google.com> Cc: Brian Geffon <bgeffon@google.com> Cc: Christian Brauner <brauner@kernel.org> Cc: David Hildenbrand <david@redhat.com> Cc: Hugh Dickins <hughd@google.com> Cc: Jann Horn <jannh@google.com> Cc: Kalesh Singh <kaleshsingh@google.com> Cc: kernel-team@android.com Cc: Liam R. Howlett <Liam.Howlett@oracle.com> Cc: Lokesh Gidra <lokeshgidra@google.com> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Michal Hocko <mhocko@suse.com> Cc: Mike Rapoport (IBM) <rppt@kernel.org> Cc: Nicolas Geoffray <ngeoffray@google.com> Cc: Ryan Roberts <ryan.roberts@arm.com> Cc: Shuah Khan <shuah@kernel.org> Cc: ZhangPeng <zhangpeng362@huawei.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Matthew Wilcox (Oracle) [Thu, 9 Nov 2023 21:06:08 +0000 (21:06 +0000)]
buffer: fix more functions for block size > PAGE_SIZE
Both __block_write_full_folio() and block_read_full_folio() assumed that
block size <= PAGE_SIZE. Replace the shift with a divide, which is
probably cheaper than first calculating the shift. That lets us remove
block_size_bits() as these were the last callers.
Link: https://lkml.kernel.org/r/20231109210608.2252323-8-willy@infradead.org Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Hannes Reinecke <hare@suse.de> Cc: Luis Chamberlain <mcgrof@kernel.org> Cc: Pankaj Raghav <p.raghav@samsung.com> Cc: Ryusuke Konishi <konishi.ryusuke@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Matthew Wilcox (Oracle) [Thu, 9 Nov 2023 21:06:07 +0000 (21:06 +0000)]
buffer: handle large folios in __block_write_begin_int()
When __block_write_begin_int() was converted to support folios, we did not
expect large folios to be passed to it. With the current work to support
large block size storage devices, this will no longer be true so change
the checks on 'from' and 'to' to be related to the size of the folio
instead of PAGE_SIZE. Also remove an assumption that the block size is
smaller than PAGE_SIZE.
Link: https://lkml.kernel.org/r/20231109210608.2252323-7-willy@infradead.org Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org> Reported-by: Ryusuke Konishi <konishi.ryusuke@gmail.com> Cc: Hannes Reinecke <hare@suse.de> Cc: Luis Chamberlain <mcgrof@kernel.org> Cc: Pankaj Raghav <p.raghav@samsung.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Matthew Wilcox (Oracle) [Thu, 9 Nov 2023 21:06:06 +0000 (21:06 +0000)]
buffer: fix various functions for block size > PAGE_SIZE
If i_blkbits is larger than PAGE_SHIFT, we shift by a negative number,
which is undefined. It is safe to shift the block left as a block device
must be smaller than MAX_LFS_FILESIZE, which is guaranteed to fit in
loff_t.
Link: https://lkml.kernel.org/r/20231109210608.2252323-6-willy@infradead.org Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org> Reviewed-by: Pankaj Raghav <p.raghav@samsung.com> Cc: Hannes Reinecke <hare@suse.de> Cc: Luis Chamberlain <mcgrof@kernel.org> Cc: Ryusuke Konishi <konishi.ryusuke@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Matthew Wilcox (Oracle) [Thu, 9 Nov 2023 21:06:04 +0000 (21:06 +0000)]
buffer: fix grow_buffers() for block size > PAGE_SIZE
We must not shift by a negative number so work in terms of a byte offset
to avoid the awkward shift left-or-right-depending-on-sign option. This
means we need to use check_mul_overflow() to ensure that a large block
number does not result in a wrap.
Matthew Wilcox (Oracle) [Thu, 9 Nov 2023 21:06:03 +0000 (21:06 +0000)]
buffer: calculate block number inside folio_init_buffers()
The calculation of block from index doesn't work for devices with a block
size larger than PAGE_SIZE as we end up shifting by a negative number.
Instead, calculate the number of the first block from the folio's position
in the block device. We no longer need to pass sizebits to
grow_dev_folio().
Link: https://lkml.kernel.org/r/20231109210608.2252323-3-willy@infradead.org Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org> Reviewed-by: Pankaj Raghav <p.raghav@samsung.com> Cc: Hannes Reinecke <hare@suse.de> Cc: Luis Chamberlain <mcgrof@kernel.org> Cc: Ryusuke Konishi <konishi.ryusuke@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Matthew Wilcox (Oracle) [Thu, 9 Nov 2023 21:06:02 +0000 (21:06 +0000)]
buffer: return bool from grow_dev_folio()
Patch series "More buffer_head cleanups", v2.
The first patch is a left-over from last cycle. The rest fix "obvious"
block size > PAGE_SIZE problems. I haven't tested with a large block size
setup (but I have done an ext4 xfstests run).
This patch (of 7):
Rename grow_dev_page() to grow_dev_folio() and make it return a bool.
Document what that bool means; it's more subtle than it first appears.
Also rename the 'failed' label to 'unlock' beacuse it's not exactly
'failed'. It just hasn't succeeded.
Link: https://lkml.kernel.org/r/20231109210608.2252323-2-willy@infradead.org Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Hannes Reinecke <hare@suse.de> Cc: Luis Chamberlain <mcgrof@kernel.org> Cc: Pankaj Raghav <p.raghav@samsung.com> Cc: Ryusuke Konishi <konishi.ryusuke@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Peng Zhang [Fri, 15 Dec 2023 07:46:32 +0000 (15:46 +0800)]
maple_tree: avoid checking other gaps after getting the largest gap
The last range stored in maple tree is typically quite large. By checking
if it exceeds the sum of the remaining ranges in that node, it is possible
to avoid checking all other gaps.
Running the maple tree test suite in user mode almost always results in a
near 100% hit rate for this optimization.
Fabio M. De Francesco [Thu, 14 Dec 2023 08:10:04 +0000 (09:10 +0100)]
mm/memory: replace kmap() with kmap_local_page()
kmap() has been deprecated in favor of kmap_local_page().
Therefore, replace kmap() with kmap_local_page() in mm/memory.c.
There are two main problems with kmap(): (1) It comes with an overhead as
the mapping space is restricted and protected by a global lock for
synchronization and (2) it also requires global TLB invalidation when the
kmap's pool wraps and it might block when the mapping space is fully
utilized until a slot becomes available.
With kmap_local_page() the mappings are per thread, CPU local, can take
page-faults, and can be called from any context (including interrupts).
It is faster than kmap() in kernels with HIGHMEM enabled. The tasks can
be preempted and, when they are scheduled to run again, the kernel virtual
addresses are restored and still valid.
Obviously, thread locality implies that the kernel virtual addresses
returned by kmap_local_page() are only valid in the context of the callers
(i.e., they cannot be handed to other threads).
The use of kmap_local_page() in mm/memory.c does not break the
above-mentioned assumption, so it is allowed and preferred.
SeongJae Park [Wed, 13 Dec 2023 19:03:38 +0000 (19:03 +0000)]
Docs/admin-guide/mm/damon/usage: use a list for 'state' sysfs file input commands
There are eight command inputs for 'state' DAMON sysfs file, and those are
verbosely explained in multiple paragraphs. It is not easy to find
explanation of specific command, and getting whole picture of supported
commands. Replace the paragraphs with a list.
SeongJae Park [Wed, 13 Dec 2023 19:03:37 +0000 (19:03 +0000)]
Docs/admin-guide/mm/damon/usage: add links to sysfs files hierarchy
'Sysfs Files Hierarchy' section of DAMON usage document shows whole
picture of the interface. Then sections for detailed explanation of the
files follow. Due to the amount of the files, navigating between the
whole picture and the section for specific files sometimes require no
subtle amount of scrolling. Add links from the whole picture to the
dedicated sections for making the navigation easier.
The label for context DAMON sysfs directory section is having name
sysfs_contexts. The name would be better to be used for the contexts
directory. Rename it to represent a single context.
SeongJae Park [Wed, 13 Dec 2023 19:03:35 +0000 (19:03 +0000)]
Docs/mm/damon/design: place execution model and data structures at the beginning
The execution model and data structures section at the end of the design
document is briefly explaining how DAMON works overall. Knowing that
first may help better drawing the overall picture. It may also help
better understanding following detailed sections. Move it to the
beginning of the document.
SeongJae Park [Wed, 13 Dec 2023 19:03:34 +0000 (19:03 +0000)]
mm/damon/core-test: test max_nr_accesses overflow caused divide-by-zero
Commit 35f5d94187a6 ("mm/damon: implement a function for max nr_accesses
safe calculation") has fixed an overflow bug that could cause
divide-by-zero. Add a kunit test for the bug to ensure similar bugs are
not introduced again.
Kevin Hao [Wed, 13 Dec 2023 09:09:06 +0000 (17:09 +0800)]
mm: ksm: remove unnecessary try_to_freeze()
A freezable kernel thread can enter frozen state during freezing by
either calling try_to_freeze() or using wait_event_freezable() and its
variants. However, there is no need to use both methods simultaneously.
Link: https://lkml.kernel.org/r/20231213090906.1070985-1-haokexin@gmail.com Signed-off-by: Kevin Hao <haokexin@gmail.com> Acked-by: David Hildenbrand <david@redhat.com> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: "Rafael J. Wysocki" <rafael@kernel.org> Cc: Pavel Machek <pavel@ucw.cz> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
SeongJae Park [Tue, 12 Dec 2023 19:48:10 +0000 (19:48 +0000)]
selftests/damon: add a test for update_schemes_tried_regions hang bug
Add a test for reproducing the update_schemes_tried_{regions,bytes}
command-causing indefinite hang bug that fixed by commit 7d6fa31a2fd7
("mm/damon/sysfs-schemes: add timeout for update_schemes_tried_regions"),
to avoid mistakenly re-introducing the bug. Refer to the fix commit for
more details of the bug.
SeongJae Park [Tue, 12 Dec 2023 19:48:09 +0000 (19:48 +0000)]
selftests/damon: add a test for update_schemes_tried_regions sysfs command
Add a selftest for verifying the accuracy of DAMON's access monitoring
functionality. The test starts a program of artificial access pattern,
monitor the access pattern using DAMON, and check if DAMON finds expected
amount of hot data region (working set size) with only acceptable error
rate.
Note that the acceptable error rate is set with only naive assumptions and
small number of tests. Hence failures of the test may not always mean
DAMON is broken. Rather than that, those could be a signal to better
understand the real accuracy level of DAMON in wider environments. Based
on further finding, we could optimize DAMON or adjust the expectation of
the test.
Implement update_schemes_tried_bytes command of DAMON sysfs interface in
_damon_sysfs.py. It is not only making the update, but also read the
updated value from the sysfs interface and store it in the Kdamond python
objects so that the user of the module can easily get the value.
SeongJae Park [Tue, 12 Dec 2023 19:48:06 +0000 (19:48 +0000)]
selftests/damon: implement a python module for test-purpose DAMON sysfs controls
Patch series "selftests/damon: add Python-written DAMON functionality
tests", v2.
DAMON exports most of its functionality via its sysfs interface. Hence
most DAMON functionality tests could be implemented using the interface.
However, because the interfaces require simple but multiple operations for
many controls, writing all such tests from the scratch could be repetitive
and time consuming.
Implement a minimum DAMON sysfs control module, and a couple of DAMON
functionality tests using the control module. The first test is for
ensuring minimum accuracy of data access monitoring, and the second test
is for finding if a previously found and fixed bug is introduced again.
Note that the DAMON sysfs control module is only for avoiding duplicating
code in tests. For convenient and general control of DAMON, users should
use DAMON user-space tools that developed for the purpose, such as
damo[1].
[1] https://github.com/damonitor/damo
Patches Sequence
----------------
This patchset is constructed with five patches. The first three patches
implement a Python-written test implementation-purpose DAMON sysfs control
module. The implementation is incrementally done in the sequence of the
basic data structure (first patch) first, kdamonds start command (second
patch) next, and finally DAMOS tried bytes update command (third patch).
Then two patches for implementing selftests using the module follows. The
fourth patch implements a basic functionality test of DAMON for working
set estimation accuracy. Finally, the fifth patch implements a corner
case test for a previously found bug.
This patch (of 5):
Implement a python module for DAMON sysfs controls. The module is aimed
to be useful for writing DAMON functionality tests in future.
Nonetheless, this module is only representing a subset of DAMON sysfs
files. Following commits will implement more DAMON sysfs controls.
Randy Dunlap [Sun, 10 Dec 2023 06:38:39 +0000 (22:38 -0800)]
maple_tree: fix typos/spellos etc
Fix typos/grammar and spellos in documentation.
Link: https://lkml.kernel.org/r/20231210063839.29967-1-rdunlap@infradead.org Signed-off-by: Randy Dunlap <rdunlap@infradead.org> Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Liam R. Howlett <Liam.Howlett@oracle.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Ryan Roberts [Thu, 7 Dec 2023 16:12:11 +0000 (16:12 +0000)]
selftests/mm/cow: add tests for anonymous multi-size THP
Add tests similar to the existing PMD-sized THP tests, but which operate
on memory backed by (PTE-mapped) multi-size THP. This reuses all the
existing infrastructure. If the test suite detects that multi-size THP is
not supported by the kernel, the new tests are skipped.
Link: https://lkml.kernel.org/r/20231207161211.2374093-11-ryan.roberts@arm.com Signed-off-by: Ryan Roberts <ryan.roberts@arm.com> Reviewed-by: David Hildenbrand <david@redhat.com> Tested-by: Kefeng Wang <wangkefeng.wang@huawei.com> Tested-by: John Hubbard <jhubbard@nvidia.com> Cc: Alistair Popple <apopple@nvidia.com> Cc: Anshuman Khandual <anshuman.khandual@arm.com> Cc: Barry Song <v-songbaohua@oppo.com> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: David Rientjes <rientjes@google.com> Cc: "Huang, Ying" <ying.huang@intel.com> Cc: Hugh Dickins <hughd@google.com> Cc: Itaru Kitayama <itaru.kitayama@gmail.com> Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Luis Chamberlain <mcgrof@kernel.org> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: Yang Shi <shy828301@gmail.com> Cc: Yin Fengwei <fengwei.yin@intel.com> Cc: Yu Zhao <yuzhao@google.com> Cc: Zi Yan <ziy@nvidia.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
do_run_with_thp() prepares (PMD-sized) THP memory into different states
before running tests. With the introduction of multi-size THP, we would
like to reuse this logic to also test those smaller THP sizes. So let's
add a thpsize parameter which tells the function what size THP it should
operate on.
A separate commit will utilize this change to add new tests for multi-size
THP, where available.
Link: https://lkml.kernel.org/r/20231207161211.2374093-10-ryan.roberts@arm.com Signed-off-by: Ryan Roberts <ryan.roberts@arm.com> Reviewed-by: David Hildenbrand <david@redhat.com> Tested-by: Kefeng Wang <wangkefeng.wang@huawei.com> Tested-by: John Hubbard <jhubbard@nvidia.com> Cc: Alistair Popple <apopple@nvidia.com> Cc: Anshuman Khandual <anshuman.khandual@arm.com> Cc: Barry Song <v-songbaohua@oppo.com> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: David Rientjes <rientjes@google.com> Cc: "Huang, Ying" <ying.huang@intel.com> Cc: Hugh Dickins <hughd@google.com> Cc: Itaru Kitayama <itaru.kitayama@gmail.com> Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Luis Chamberlain <mcgrof@kernel.org> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: Yang Shi <shy828301@gmail.com> Cc: Yin Fengwei <fengwei.yin@intel.com> Cc: Yu Zhao <yuzhao@google.com> Cc: Zi Yan <ziy@nvidia.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Ryan Roberts [Thu, 7 Dec 2023 16:12:09 +0000 (16:12 +0000)]
selftests/mm/khugepaged: enlighten for multi-size THP
The `collapse_max_ptes_none` test was previously failing when a THP size
less than PMD-size had enabled="always". The root cause is because the
test faults in 1 page less than the threshold it set for collapsing. But
when THP is enabled always, we "over allocate" and therefore the threshold
is passed, and collapse unexpectedly succeeds.
Solve this by enlightening khugepaged selftest. Add a command line option
to pass in the desired THP size that should be used for all anonymous
allocations. The harness will then explicitly configure a THP size as
requested and modify the `collapse_max_ptes_none` test so that it faults
in the threshold minus the number of pages in the configured THP size. If
no command line option is provided, default to order 0, as per previous
behaviour.
I chose to use an order in the command line interface, since this makes
the interface agnostic of base page size, making it easier to invoke from
run_vmtests.sh.
Link: https://lkml.kernel.org/r/20231207161211.2374093-9-ryan.roberts@arm.com Signed-off-by: Ryan Roberts <ryan.roberts@arm.com> Tested-by: Kefeng Wang <wangkefeng.wang@huawei.com> Tested-by: John Hubbard <jhubbard@nvidia.com> Cc: Alistair Popple <apopple@nvidia.com> Cc: Anshuman Khandual <anshuman.khandual@arm.com> Cc: Barry Song <v-songbaohua@oppo.com> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: David Hildenbrand <david@redhat.com> Cc: David Rientjes <rientjes@google.com> Cc: "Huang, Ying" <ying.huang@intel.com> Cc: Hugh Dickins <hughd@google.com> Cc: Itaru Kitayama <itaru.kitayama@gmail.com> Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Luis Chamberlain <mcgrof@kernel.org> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: Yang Shi <shy828301@gmail.com> Cc: Yin Fengwei <fengwei.yin@intel.com> Cc: Yu Zhao <yuzhao@google.com> Cc: Zi Yan <ziy@nvidia.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Ryan Roberts [Thu, 7 Dec 2023 16:12:08 +0000 (16:12 +0000)]
selftests/mm: support multi-size THP interface in thp_settings
Save and restore the new per-size hugepage enabled setting, if available
on the running kernel.
Since the number of per-size directories is not fixed, solve this as
simply as possible by catering for a maximum number in the thp_settings
struct (20). Each array index is the order. The value of THP_NEVER is
changed to 0 so that all of these new settings default to THP_NEVER and
the user only needs to fill in the ones they want to enable.
Link: https://lkml.kernel.org/r/20231207161211.2374093-8-ryan.roberts@arm.com Signed-off-by: Ryan Roberts <ryan.roberts@arm.com> Tested-by: Kefeng Wang <wangkefeng.wang@huawei.com> Tested-by: John Hubbard <jhubbard@nvidia.com> Cc: Alistair Popple <apopple@nvidia.com> Cc: Anshuman Khandual <anshuman.khandual@arm.com> Cc: Barry Song <v-songbaohua@oppo.com> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: David Hildenbrand <david@redhat.com> Cc: David Rientjes <rientjes@google.com> Cc: "Huang, Ying" <ying.huang@intel.com> Cc: Hugh Dickins <hughd@google.com> Cc: Itaru Kitayama <itaru.kitayama@gmail.com> Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Luis Chamberlain <mcgrof@kernel.org> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: Yang Shi <shy828301@gmail.com> Cc: Yin Fengwei <fengwei.yin@intel.com> Cc: Yu Zhao <yuzhao@google.com> Cc: Zi Yan <ziy@nvidia.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Ryan Roberts [Thu, 7 Dec 2023 16:12:07 +0000 (16:12 +0000)]
selftests/mm: factor out thp settings management
The khugepaged test has a useful framework for save/restore/pop/push of
all thp settings via the sysfs interface. This will be useful to
explicitly control multi-size THP settings in other tests, so let's move
it out of khugepaged and into its own thp_settings.[c|h] utility.
Link: https://lkml.kernel.org/r/20231207161211.2374093-7-ryan.roberts@arm.com Signed-off-by: Ryan Roberts <ryan.roberts@arm.com> Tested-by: Alistair Popple <apopple@nvidia.com> Acked-by: David Hildenbrand <david@redhat.com> Tested-by: Kefeng Wang <wangkefeng.wang@huawei.com> Tested-by: John Hubbard <jhubbard@nvidia.com> Cc: Anshuman Khandual <anshuman.khandual@arm.com> Cc: Barry Song <v-songbaohua@oppo.com> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: David Rientjes <rientjes@google.com> Cc: "Huang, Ying" <ying.huang@intel.com> Cc: Hugh Dickins <hughd@google.com> Cc: Itaru Kitayama <itaru.kitayama@gmail.com> Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Luis Chamberlain <mcgrof@kernel.org> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: Yang Shi <shy828301@gmail.com> Cc: Yin Fengwei <fengwei.yin@intel.com> Cc: Yu Zhao <yuzhao@google.com> Cc: Zi Yan <ziy@nvidia.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Ryan Roberts [Thu, 7 Dec 2023 16:12:06 +0000 (16:12 +0000)]
selftests/mm/kugepaged: restore thp settings at exit
Previously, the saved thp settings would be restored upon a signal or at
the natural end of the test suite. But there are some tests that directly
call exit() upon failure. In this case, the thp settings were not being
restored, which could then influence other tests.
Fix this by installing an atexit() handler to do the actual restore. The
signal handler can now just call exit() and the atexit handler is invoked.
Link: https://lkml.kernel.org/r/20231207161211.2374093-6-ryan.roberts@arm.com Signed-off-by: Ryan Roberts <ryan.roberts@arm.com> Reviewed-by: Alistair Popple <apopple@nvidia.com> Reviewed-by: David Hildenbrand <david@redhat.com> Tested-by: Kefeng Wang <wangkefeng.wang@huawei.com> Tested-by: John Hubbard <jhubbard@nvidia.com> Cc: Anshuman Khandual <anshuman.khandual@arm.com> Cc: Barry Song <v-songbaohua@oppo.com> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: David Rientjes <rientjes@google.com> Cc: "Huang, Ying" <ying.huang@intel.com> Cc: Hugh Dickins <hughd@google.com> Cc: Itaru Kitayama <itaru.kitayama@gmail.com> Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Luis Chamberlain <mcgrof@kernel.org> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: Yang Shi <shy828301@gmail.com> Cc: Yin Fengwei <fengwei.yin@intel.com> Cc: Yu Zhao <yuzhao@google.com> Cc: Zi Yan <ziy@nvidia.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Ryan Roberts [Thu, 7 Dec 2023 16:12:05 +0000 (16:12 +0000)]
mm: thp: support allocation of anonymous multi-size THP
Introduce the logic to allow THP to be configured (through the new sysfs
interface we just added) to allocate large folios to back anonymous
memory, which are larger than the base page size but smaller than
PMD-size. We call this new THP extension "multi-size THP" (mTHP).
mTHP continues to be PTE-mapped, but in many cases can still provide
similar benefits to traditional PMD-sized THP: Page faults are
significantly reduced (by a factor of e.g. 4, 8, 16, etc. depending on
the configured order), but latency spikes are much less prominent because
the size of each page isn't as huge as the PMD-sized variant and there is
less memory to clear in each page fault. The number of per-page
operations (e.g. ref counting, rmap management, lru list management) are
also significantly reduced since those ops now become per-folio.
Some architectures also employ TLB compression mechanisms to squeeze more
entries in when a set of PTEs are virtually and physically contiguous and
approporiately aligned. In this case, TLB misses will occur less often.
The new behaviour is disabled by default, but can be enabled at runtime by
writing to /sys/kernel/mm/transparent_hugepage/hugepage-XXkb/enabled (see
documentation in previous commit). The long term aim is to change the
default to include suitable lower orders, but there are some risks around
internal fragmentation that need to be better understood first.
[ryan.roberts@arm.com: resolve some multi-size THP review nits] Link: https://lkml.kernel.org/r/20231214160251.3574571-1-ryan.roberts@arm.com Link: https://lkml.kernel.org/r/20231207161211.2374093-5-ryan.roberts@arm.com Signed-off-by: Ryan Roberts <ryan.roberts@arm.com> Tested-by: Kefeng Wang <wangkefeng.wang@huawei.com> Tested-by: John Hubbard <jhubbard@nvidia.com> Acked-by: David Hildenbrand <david@redhat.com> Cc: Alistair Popple <apopple@nvidia.com> Cc: Anshuman Khandual <anshuman.khandual@arm.com> Cc: Barry Song <v-songbaohua@oppo.com> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: David Rientjes <rientjes@google.com> Cc: "Huang, Ying" <ying.huang@intel.com> Cc: Hugh Dickins <hughd@google.com> Cc: Itaru Kitayama <itaru.kitayama@gmail.com> Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Luis Chamberlain <mcgrof@kernel.org> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: Yang Shi <shy828301@gmail.com> Cc: Yin Fengwei <fengwei.yin@intel.com> Cc: Yu Zhao <yuzhao@google.com> Cc: Zi Yan <ziy@nvidia.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Ryan Roberts [Thu, 7 Dec 2023 16:12:04 +0000 (16:12 +0000)]
mm: thp: introduce multi-size THP sysfs interface
In preparation for adding support for anonymous multi-size THP, introduce
new sysfs structure that will be used to control the new behaviours. A
new directory is added under transparent_hugepage for each supported THP
size, and contains an `enabled` file, which can be set to "inherit" (to
inherit the global setting), "always", "madvise" or "never". For now, the
kernel still only supports PMD-sized anonymous THP, so only 1 directory is
populated.
The first half of the change converts transhuge_vma_suitable() and
hugepage_vma_check() so that they take a bitfield of orders for which the
user wants to determine support, and the functions filter out all the
orders that can't be supported, given the current sysfs configuration and
the VMA dimensions. The resulting functions are renamed to
thp_vma_suitable_orders() and thp_vma_allowable_orders() respectively.
Convenience functions that take a single, unencoded order and return a
boolean are also defined as thp_vma_suitable_order() and
thp_vma_allowable_order().
The second half of the change implements the new sysfs interface. It has
been done so that each supported THP size has a `struct thpsize`, which
describes the relevant metadata and is itself a kobject. This is pretty
minimal for now, but should make it easy to add new per-thpsize files to
the interface if needed in future (e.g. per-size defrag). Rather than
keep the `enabled` state directly in the struct thpsize, I've elected to
directly encode it into huge_anon_orders_[always|madvise|inherit]
bitfields since this reduces the amount of work required in
thp_vma_allowable_orders() which is called for every page fault.
See Documentation/admin-guide/mm/transhuge.rst, as modified by this
commit, for details of how the new sysfs interface works.
[ryan.roberts@arm.com: fix build warning when CONFIG_SYSFS is disabled] Link: https://lkml.kernel.org/r/20231211125320.3997543-1-ryan.roberts@arm.com Link: https://lkml.kernel.org/r/20231207161211.2374093-4-ryan.roberts@arm.com Signed-off-by: Ryan Roberts <ryan.roberts@arm.com> Reviewed-by: Barry Song <v-songbaohua@oppo.com> Tested-by: Kefeng Wang <wangkefeng.wang@huawei.com> Tested-by: John Hubbard <jhubbard@nvidia.com> Acked-by: David Hildenbrand <david@redhat.com> Cc: Alistair Popple <apopple@nvidia.com> Cc: Anshuman Khandual <anshuman.khandual@arm.com> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: David Rientjes <rientjes@google.com> Cc: "Huang, Ying" <ying.huang@intel.com> Cc: Hugh Dickins <hughd@google.com> Cc: Itaru Kitayama <itaru.kitayama@gmail.com> Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Luis Chamberlain <mcgrof@kernel.org> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: Yang Shi <shy828301@gmail.com> Cc: Yin Fengwei <fengwei.yin@intel.com> Cc: Yu Zhao <yuzhao@google.com> Cc: Zi Yan <ziy@nvidia.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Ryan Roberts [Thu, 7 Dec 2023 16:12:03 +0000 (16:12 +0000)]
mm: non-pmd-mappable, large folios for folio_add_new_anon_rmap()
In preparation for supporting anonymous multi-size THP, improve
folio_add_new_anon_rmap() to allow a non-pmd-mappable, large folio to be
passed to it. In this case, all contained pages are accounted using the
order-0 folio (or base page) scheme.
Link: https://lkml.kernel.org/r/20231207161211.2374093-3-ryan.roberts@arm.com Signed-off-by: Ryan Roberts <ryan.roberts@arm.com> Reviewed-by: Yu Zhao <yuzhao@google.com> Reviewed-by: Yin Fengwei <fengwei.yin@intel.com> Reviewed-by: David Hildenbrand <david@redhat.com> Reviewed-by: Barry Song <v-songbaohua@oppo.com> Tested-by: Kefeng Wang <wangkefeng.wang@huawei.com> Tested-by: John Hubbard <jhubbard@nvidia.com> Cc: Alistair Popple <apopple@nvidia.com> Cc: Anshuman Khandual <anshuman.khandual@arm.com> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: David Rientjes <rientjes@google.com> Cc: "Huang, Ying" <ying.huang@intel.com> Cc: Hugh Dickins <hughd@google.com> Cc: Itaru Kitayama <itaru.kitayama@gmail.com> Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Luis Chamberlain <mcgrof@kernel.org> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: Yang Shi <shy828301@gmail.com> Cc: Zi Yan <ziy@nvidia.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Ryan Roberts [Thu, 7 Dec 2023 16:12:02 +0000 (16:12 +0000)]
mm: allow deferred splitting of arbitrary anon large folios
Patch series "Multi-size THP for anonymous memory", v9.
A series to implement multi-size THP (mTHP) for anonymous memory
(previously called "small-sized THP" and "large anonymous folios").
The objective of this is to improve performance by allocating larger
chunks of memory during anonymous page faults:
1) Since SW (the kernel) is dealing with larger chunks of memory than base
pages, there are efficiency savings to be had; fewer page faults, batched PTE
and RMAP manipulation, reduced lru list, etc. In short, we reduce kernel
overhead. This should benefit all architectures.
2) Since we are now mapping physically contiguous chunks of memory, we can take
advantage of HW TLB compression techniques. A reduction in TLB pressure
speeds up kernel and user space. arm64 systems have 2 mechanisms to coalesce
TLB entries; "the contiguous bit" (architectural) and HPA (uarch).
This version incorporates David's feedback on the core patches (#3, #4)
and adds some RB and TB tags (see change log for details).
By default, the existing behaviour (and performance) is maintained. The
user must explicitly enable multi-size THP to see the performance benefit.
This is done via a new sysfs interface (as recommended by David
Hildenbrand - thanks to David for the suggestion)! This interface is
inspired by the existing per-hugepage-size sysfs interface used by
hugetlb, provides full backwards compatibility with the existing PMD-size
THP interface, and provides a base for future extensibility. See [9] for
detailed discussion of the interface.
This series is based on mm-unstable (715b67adf4c8).
Prerequisites
=============
I'm removing this section on the basis that I don't believe what we were
previously calling prerequisites are really prerequisites anymore. We
originally defined them when mTHP was a compile-time feature. There is
now a runtime control to opt-in to mTHP; when disabled, correctness and
performance are as before. When enabled, the code is still
correct/robust, but in the absence of the one remaining item (compaction)
there may be a performance impact in some corners. See the old list in
the v8 cover letter at [8]. And a longer explanation of my thinking here
[10].
SUMMARY: I don't think we should hold this series up, waiting for the
items on the prerequisites list. I believe this series should be ready
now so hopefully can be added to mm-unstable for some testing, then
fingers crossed for v6.8.
Testing
=======
The series includes patches for mm selftests to enlighten the cow and
khugepaged tests to explicitly test with multi-size THP, in the same way
that PMD-sized THP is tested. The new tests all pass, and no regressions
are observed in the mm selftest suite. I've also run my usual kernel
compilation and java script benchmarks without any issues.
Refer to my performance numbers posted with v6 [6]. (These are for
multi-size THP only - they do not include the arm64 contpte follow-on
series).
John Hubbard at Nvidia has indicated dramatic 10x performance improvements
for some workloads at [11]. (Observed using v6 of this series as well as
the arm64 contpte series).
Kefeng Wang at Huawei has also indicated he sees improvements at [12] although
there are some latency regressions also.
I've also checked that there is no regression in the write fault path when
mTHP is disabled using a microbenchmark. I ran it for a baseline kernel,
as well as v8 and v9. I repeated on Ampere Altra (bare metal) and Apple
M2 (VM):
There is no measurable difference on M2, but altra has a slow down in v8
which is fixed in v9 by moving the THP order check to be inline within
thp_vma_allowable_orders(), as suggested by David.
This patch (of 10):
In preparation for the introduction of anonymous multi-size THP, we would
like to be able to split them when they have unmapped subpages, in order
to free those unused pages under memory pressure. So remove the
artificial requirement that the large folio needed to be at least
PMD-sized.
Link: https://lkml.kernel.org/r/20231207161211.2374093-1-ryan.roberts@arm.com Link: https://lkml.kernel.org/r/20231207161211.2374093-2-ryan.roberts@arm.com Signed-off-by: Ryan Roberts <ryan.roberts@arm.com> Reviewed-by: Yu Zhao <yuzhao@google.com> Reviewed-by: Yin Fengwei <fengwei.yin@intel.com> Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org> Reviewed-by: David Hildenbrand <david@redhat.com> Reviewed-by: Barry Song <v-songbaohua@oppo.com> Tested-by: Kefeng Wang <wangkefeng.wang@huawei.com> Tested-by: John Hubbard <jhubbard@nvidia.com> Cc: Alistair Popple <apopple@nvidia.com> Cc: Anshuman Khandual <anshuman.khandual@arm.com> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: David Rientjes <rientjes@google.com> Cc: "Huang, Ying" <ying.huang@intel.com> Cc: Hugh Dickins <hughd@google.com> Cc: Itaru Kitayama <itaru.kitayama@gmail.com> Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Luis Chamberlain <mcgrof@kernel.org> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: Yang Shi <shy828301@gmail.com> Cc: Zi Yan <ziy@nvidia.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Yosry Ahmed [Wed, 29 Nov 2023 03:21:53 +0000 (03:21 +0000)]
mm: memcg: restore subtree stats flushing
Stats flushing for memcg currently follows the following rules:
- Always flush the entire memcg hierarchy (i.e. flush the root).
- Only one flusher is allowed at a time. If someone else tries to flush
concurrently, they skip and return immediately.
- A periodic flusher flushes all the stats every 2 seconds.
The reason this approach is followed is because all flushes are serialized
by a global rstat spinlock. On the memcg side, flushing is invoked from
userspace reads as well as in-kernel flushers (e.g. reclaim, refault,
etc). This approach aims to avoid serializing all flushers on the global
lock, which can cause a significant performance hit under high
concurrency.
This approach has the following problems:
- Occasionally a userspace read of the stats of a non-root cgroup will
be too expensive as it has to flush the entire hierarchy [1].
- Sometimes the stats accuracy are compromised if there is an ongoing
flush, and we skip and return before the subtree of interest is
actually flushed, yielding stale stats (by up to 2s due to periodic
flushing). This is more visible when reading stats from userspace,
but can also affect in-kernel flushers.
The latter problem is particulary a concern when userspace reads stats
after an event occurs, but gets stats from before the event. Examples:
- When memory usage / pressure spikes, a userspace OOM handler may look
at the stats of different memcgs to select a victim based on various
heuristics (e.g. how much private memory will be freed by killing
this). Reading stale stats from before the usage spike in this case
may cause a wrongful OOM kill.
- A proactive reclaimer may read the stats after writing to
memory.reclaim to measure the success of the reclaim operation. Stale
stats from before reclaim may give a false negative.
- Reading the stats of a parent and a child memcg may be inconsistent
(child larger than parent), if the flush doesn't happen when the
parent is read, but happens when the child is read.
As for in-kernel flushers, they will occasionally get stale stats. No
regressions are currently known from this, but if there are regressions,
they would be very difficult to debug and link to the source of the
problem.
This patch aims to fix these problems by restoring subtree flushing, and
removing the unified/coalesced flushing logic that skips flushing if there
is an ongoing flush. This change would introduce a significant regression
with global stats flushing thresholds. With per-memcg stats flushing
thresholds, this seems to perform really well. The thresholds protect the
underlying lock from unnecessary contention.
This patch was tested in two ways to ensure the latency of flushing is
up to par, on a machine with 384 cpus:
- A synthetic test with 5000 concurrent workers in 500 cgroups doing
allocations and reclaim, as well as 1000 readers for memory.stat
(variation of [2]). No regressions were noticed in the total runtime.
Note that significant regressions in this test are observed with
global stats thresholds, but not with per-memcg thresholds.
- A synthetic stress test for concurrently reading memcg stats while
memory allocation/freeing workers are running in the background,
provided by Wei Xu [3]. With 250k threads reading the stats every
100ms in 50k cgroups, 99.9% of reads take <= 50us. Less than 0.01%
of reads take more than 1ms, and no reads take more than 100ms.
Yosry Ahmed [Wed, 29 Nov 2023 03:21:52 +0000 (03:21 +0000)]
mm: workingset: move the stats flush into workingset_test_recent()
The workingset code flushes the stats in workingset_refault() to get
accurate stats of the eviction memcg. In preparation for more scoped
flushed and passing the eviction memcg to the flush call, move the call to
workingset_test_recent() where we have a pointer to the eviction memcg.
The flush call is sleepable, and cannot be made in an rcu read section.
Hence, minimize the rcu read section by also moving it into
workingset_test_recent(). Furthermore, instead of holding the rcu read
lock throughout workingset_test_recent(), only hold it briefly to get a
ref on the eviction memcg. This allows us to make the flush call after we
get the eviction memcg.
As for workingset_refault(), nothing else there appears to be protected by
rcu. The memcg of the faulted folio (which is not necessarily the same as
the eviction memcg) is protected by the folio lock, which is held from all
callsites. Add a VM_BUG_ON() to make sure this doesn't change from under
us.
No functional change intended.
Link: https://lkml.kernel.org/r/20231129032154.3710765-5-yosryahmed@google.com Signed-off-by: Yosry Ahmed <yosryahmed@google.com> Tested-by: Domenico Cerasuolo <cerasuolodomenico@gmail.com> Acked-by: Shakeel Butt <shakeelb@google.com> Cc: Chris Li <chrisl@kernel.org> Cc: Greg Thelen <gthelen@google.com> Cc: Ivan Babrou <ivan@cloudflare.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Michal Hocko <mhocko@kernel.org> Cc: Michal Koutny <mkoutny@suse.com> Cc: Muchun Song <muchun.song@linux.dev> Cc: Roman Gushchin <roman.gushchin@linux.dev> Cc: Tejun Heo <tj@kernel.org> Cc: Waiman Long <longman@redhat.com> Cc: Wei Xu <weixugc@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Yosry Ahmed [Wed, 29 Nov 2023 03:21:51 +0000 (03:21 +0000)]
mm: memcg: make stats flushing threshold per-memcg
A global counter for the magnitude of memcg stats update is maintained on
the memcg side to avoid invoking rstat flushes when the pending updates
are not significant. This avoids unnecessary flushes, which are not very
cheap even if there isn't a lot of stats to flush. It also avoids
unnecessary lock contention on the underlying global rstat lock.
Make this threshold per-memcg. The scheme is followed where percpu (now
also per-memcg) counters are incremented in the update path, and only
propagated to per-memcg atomics when they exceed a certain threshold.
This provides two benefits: (a) On large machines with a lot of memcgs,
the global threshold can be reached relatively fast, so guarding the
underlying lock becomes less effective. Making the threshold per-memcg
avoids this.
(b) Having a global threshold makes it hard to do subtree flushes, as we
cannot reset the global counter except for a full flush. Per-memcg
counters removes this as a blocker from doing subtree flushes, which helps
avoid unnecessary work when the stats of a small subtree are needed.
Nothing is free, of course. This comes at a cost: (a) A new per-cpu
counter per memcg, consuming NR_CPUS * NR_MEMCGS * 4 bytes. The extra
memory usage is insigificant.
(b) More work on the update side, although in the common case it will only
be percpu counter updates. The amount of work scales with the number of
ancestors (i.e. tree depth). This is not a new concept, adding a cgroup
to the rstat tree involves a parent loop, so is charging. Testing results
below show no significant regressions.
(c) The error margin in the stats for the system as a whole increases from
NR_CPUS * MEMCG_CHARGE_BATCH to NR_CPUS * MEMCG_CHARGE_BATCH * NR_MEMCGS.
This is probably fine because we have a similar per-memcg error in charges
coming from percpu stocks, and we have a periodic flusher that makes sure
we always flush all the stats every 2s anyway.
This patch was tested to make sure no significant regressions are
introduced on the update path as follows. The following benchmarks were
ran in a cgroup that is 2 levels deep (/sys/fs/cgroup/a/b/):
(1) Running 22 instances of netperf on a 44 cpu machine with
hyperthreading disabled. All instances are run in a level 2 cgroup, as
well as netserver:
# netserver -6
# netperf -6 -H ::1 -l 60 -t TCP_SENDFILE -- -m 10K
Averaging 20 runs, the numbers are as follows:
Base: 40198.0 mbps
Patched: 38629.7 mbps (-3.9%)
The regression is minimal, especially for 22 instances in the same
cgroup sharing all ancestors (so updating the same atomics).
(2) will-it-scale page_fault tests. These tests (specifically
per_process_ops in page_fault3 test) detected a 25.9% regression before
for a change in the stats update path [1]. These are the
numbers from 10 runs (+ is good) on a machine with 256 cpus:
All regressions seem to be minimal, and within the normal variance for the
benchmark. The fix for [1] assumes that 3% is noise -- and there were no
further practical complaints), so hopefully this means that such
variations in these microbenchmarks do not reflect on practical workloads.
(3) I also ran stress-ng in a nested cgroup and did not observe any
obvious regressions.
The following patch will make use of those structs in the flushing code,
so move their definitions (and a few other dependencies) a little bit up
to reduce the diff noise in the following patch.
No functional change intended.
Link: https://lkml.kernel.org/r/20231129032154.3710765-3-yosryahmed@google.com Signed-off-by: Yosry Ahmed <yosryahmed@google.com> Tested-by: Domenico Cerasuolo <cerasuolodomenico@gmail.com> Acked-by: Shakeel Butt <shakeelb@google.com> Cc: Chris Li <chrisl@kernel.org> Cc: Greg Thelen <gthelen@google.com> Cc: Ivan Babrou <ivan@cloudflare.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Michal Hocko <mhocko@kernel.org> Cc: Michal Koutny <mkoutny@suse.com> Cc: Muchun Song <muchun.song@linux.dev> Cc: Roman Gushchin <roman.gushchin@linux.dev> Cc: Tejun Heo <tj@kernel.org> Cc: Waiman Long <longman@redhat.com> Cc: Wei Xu <weixugc@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
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